The dehydration of alcohols has been described in a lot of prior arts. U.S. Pat. No. 4,207,424 describes a process for the catalytic dehydration of alcohols to form unsaturated organic compounds in which an alcohol is dehydrated in the presence of alumina catalysts which are pre-treated with an organic silylating agent at elevated temperature. U.S. Pat. No. 4,302,357 relates to an activated alumina catalyst employed in a process for the production of ethylene from ethanol through a dehydration reaction. In the description, LHSV of ethanol is from 0.25 to 5 h−1 and preferably from 0.5 to 3 h−1. The examples are carried out at 370° C. and LHSV of 1 h−1, ethylene yield is from 65 to 94%. U.S. Pat. No. 4,232,179 relates to the preparation of ethylene, based on a process for dehydrating ethyl alcohol. More particularly, the object of said prior art is the production of ethylene in the presence of catalysts, using adiabatic reactors and a high temperature. Such adiabatic reactors may be used in parallel or may be arranged in series or arranged in assemblies of parallel series, or still only a single reactor may be used. EP 22640 relates to improved zeolite catalysts, to methods of producing such catalysts, and to their use in the conversion of ethanol and ethylene to liquid and aromatic hydrocarbons, including the conversion of ethanol to ethylene. U.S. Pat. No. 4,727,214 relates to a process for converting anhydrous or aqueous ethanol into ethylene wherein at least one catalyst of the crystalline zeolite type is used, said catalyst having, on the one hand, channels or pores formed by cycles or rings of oxygen atoms having 8 and/or 10 elements or members. U.S. Pat. No. 4,847,223 describes a catalyst comprising from 0.5 to 7% by weight of trifluoromethanesulfonic acid incorporated onto an acid-form pentasil zeolite having a Si/Al atomic ratio ranging from 5 to 54 and a process for producing the same. Also within the scope of said prior art is a process for the conversion of dilute aqueous ethanol to ethylene. U.S. Pat. No. 4,873,392 describes a process for converting diluted ethanol to ethylene which comprises heating an ethanol-containing fermentation broth thereby to vaporize a mixture of ethanol and water and contacting said vaporized mixture with a ZSM-5 zeolite catalyst.
Nitriles are present in trace quantities in olefinic hydrocarbon fractions produced in a refinery, as there are FCC and visbreakers. These nitriles tend to concentrate in the more polar stream as there is the methanol stream in an MTBE unit. The unconverted methanol enriched with nitriles is recycled back to the etherification reactor and results in enhanced poisoning of the acid etherification catalyst.
WO1997045392 provides an improved etherification process that reduces the amount of acidic ion-exchange resin catalyst that is deactivated by nitriles. This process uses a water phase to remove nitriles from a hydrocarbon phase followed by an alcohol phase to remove the nitriles from the water phase. A hydrogenation catalyst is used to convert the nitriles to amines so that they can be more easily removed from the alcohol phase.
EP 1176132 relates to a process for the etherification of olefins comprising:                bringing into contact, in a reaction zone in which is present a catalyst of the acid type and in which prevail conditions suitable for an etherification reaction, at least one alcohol and a hydrocarbon charge rich in light olefins but containing nitrogen-containing compounds which are accountable to deactivate the catalyst;        separating the effluents from the reaction zone so as to obtain at least one first fraction rich in ether and a second fraction containing the major portion of the residual alcohol and nitrogen-containing compounds;        and recycling the second fraction to the inlet of the reaction zone;said process being characterised in that, prior to it being recycled into the reaction zone, the second fraction undergoes a treatment comprising at least one step of being brought into contact with an acid adsorbent material so as to lower by at least 50% its concentration of said nitrogen-containing compounds.        
Advantageously the acid adsorbent material is chosen from the group formed by:                microporous alumina-silicates, such as the silicalites, the mordenites, the X zeolites and, preferably, the Y zeolites,        macroreticular resins grafted with acid groups (for example, sulphonic acid),        silica impregnated with acid (for example, phosphoric acid or sulphuric acid),        activated carbon, unmodified or impregnated with acid (for example, phosphoric acid or sulphuric acid),        activated alumina;        clays, unmodified or treated with an acid,        molecular sieves,        crystalline and microporous aluminophosphates,        mesoporous alumino-silicas.        
Advantageously, prior to it being brought into contact with an acid adsorbent material, the second fraction is subjected to a hydrogenation phase selective for the nitrogen-containing compounds which it contains.
These two above prior arts relate only to an etherification process, concern only the removal of the nitriles components that originate from the olefinic hydrocarbon streams and relate only to methanol in which the nitriles concentrate.
The use of alcohols coming from the biomass is of high interest. The use of raw alcohols is of interest to save the expensive steps of further distillation, dewatering by adsorption or purification. As regards the dehydration, it is made in the presence of a catalyst such as alumina or silica-alumina. Such process works well with a substantially pure ethanol such as an ethanol coming from a distillation step or dewatering step over molecular sieves by adsorption, but said distillation or adsorption step requires a lot of energy. On the other hand the use of a raw ethanol leads to a poisoning of acidic catalyst. It has been discovered that the raw ethanol contains impurities which are poisons to the dehydration catalyst or etherification catalyst.
The present invention relates in one embodiment to a purification process of the raw alcohol which doesn't require a lot of energy and prevents the poisoning of the dehydration catalyst.